Compressors increase the pressure on a fluid. As gases are compressible, the compressor also reduces the volume of a gas. A compressor stall is a local disruption of the airflow in a gas turbine or turbocharger compressor. Axi-symmetric stall, also known as compressor surge, is a breakdown in compression resulting in a reversal of flow and the violent expulsion of previously compressed gas out in the direction of the compressor intake. This condition is a result of the compressor's inability to continue working against the already-compressed gas behind it. As a result, the compressor may experience conditions that exceed its pressure rise capabilities, or the compressor may become loaded such that a flow reversal occurs, which can propagate in less than a second to include the entire compressor.
Once the compressor pressure ratio reduces to a level at which the compressor is capable of sustaining stable flow, the compressor will resume normal flow. If the conditions that induced the stall remains, the process can repeat. Repeating surge events can be dangerous, since they can cause high levels of vibration, compressor component wear and possible severe damage to compressor bearings, seals, impellers and shaft, including consequential loss of containment and explosion of hazardous gas.